This invention belongs to the genetic engineering field, and relates to novel G protein-coupled receptor proteins, genes coding for these G protein-coupled receptor proteins, methods for producing these G protein-coupled receptor proteins, screening methods using these G protein-coupled receptor proteins, antibodies for these G protein-coupled receptor proteins and screening methods using these antibodies.
Cell membrane receptors which transmit signals to the intracellular region via the activation of heterotrimeric GTP binding protein are generally referred to as xe2x80x9cG protein-coupled receptorxe2x80x9d. All members of the G protein-coupled receptor known to date are sometimes referred generally to as xe2x80x9cseven transmembrane receptorxe2x80x9d, because they form a super family having a common structure which has the extracellular amino terminus and intracellular carboxyl terminus and passes through the cell membrane seven times. The G protein-coupled receptor transmits information on various physiologically active substances from cell membranes to the intracellular region via activation of heterotrimeric GTP binding protein and subsequent changes in the intracellular second messengers induced. As the intracellular second messengers which are controlled by the heterotrimeric GTP binding protein, cAMP via adenylate cyclase, Ca++ via phospholipase C and the like are well known, and it has been revealed recently that many cellular proteins are their targets, such as the control of channels and activation of protein kinases via the heterotrimeric GTP binding protein (Gudermann, T. et al. (1997), Annu. Rev. Neurosci., 20, 399-427). The physiologically active substances that transmit information via the G protein-coupled receptor include various known physiologically active substances such as neurotransmitters, hormones, chemokine, lipid-originated signal transducers, divalent ions and proteases. Information by these physiologically active substances is transmitted to the intracellular region through their specific G protein-coupled receptor, respectively.
Several hundred types of G protein-coupled receptor have so far been cloned from eucaryote. Regarding human, hundred or more types of G protein-coupled receptor for corresponding endogenous ligands have been cloned and are regarded as targets of drugs for diseases. There are various diseases in which G protein-coupled receptor is the target, and there exist effective drugs which act upon G protein-coupled receptor, in the respective fields of central nervous system, circulatory organ system, inflammatory immune system, digestive organ system, motor organ system and urinary organ/reproductive organ system (Stadel, J. et al. (1997), Trends Pharmacol. Sci., 18, 430-437). This indicates that agonists or antagonists of G protein-coupled receptor have a high possibility of becoming a therapeutic agent of diseases, so that studies are being actively carried out on the discovery and identification of new G protein-coupled receptors.
Cloning of G protein-coupled receptor genes tends to start based on their structural homology in the super family in many cases, and a receptor having no correspondence to endogenous ligand is referred to as xe2x80x9cthe orphan G protein-coupled receptorxe2x80x9d. In general, a ligand specific for the orphan G protein-coupled receptor has not been found, so that it was difficult to develop its agonist or antagonist. In recent years, however, it has been proposed to create a drug targeting for the orphan G protein-coupled receptor by combining the substantiated compound libraries and high performance high throughout screening (Stadel, J. et al. (1997), Trends Pharmacol. Sci., 18, 430-437).
That is, it is possible to screen an agonist for an orphan G protein-coupled receptor from a compound library by effective high throughput system of the measurement of cAMP and Ca++ which are second messengers of many G protein-coupled receptors, or the measurement of GTPase activity and G protein binding of GTPxcex3S which are indexes of the activation of heterotrimeric GTP binding protein, so that it is possible to find specific agonists and antagonists making use of such compounds and furthermore to develop therapeutic drugs for certain diseases. Under such conditions, discovery of a novel G protein-coupled receptor capable of becoming a new therapeutic target of diseases is regarded as the most important step in creating a medicament which acts upon G protein-coupled receptors.
Among G protein-coupled receptors, there is a case in which a plurality of receptors are present for one endogenous ligand. Such receptors are referred to as receptor family, and each receptor is called subtype. Since all of the G protein-coupled receptors have a common structure which passes through the cell membrane seven times, 20 to 25% of amino acids are preserved mainly in the transmembrane region even in mutually independent G protein-coupled receptors, but when they form a receptor family, ratio of the amino acids preserved among its subtypes significantly increases to 35% or more, particularly to 60 to 80% among subtypes having high relevancy (Strader, C. D. et al. (1994), Annu. Rev. Biochem., 63, 101-132).
When development of a therapeutic drug for diseases is planned by targeting for an endogenous ligand wherein a receptor family is present, specificity of its subtypes becomes important in many cases. This is because actions upon other subtype than actions upon a subtype that mediates the main action of a drug lead to side effects in many cases. Accordingly, it is desirable to create a subtype-specific agonist or antagonist, but it is necessary to find a means for detecting the subtype-specificity for that purpose. Currently, a method for constructing a system in which a gene of a subtype is cloned and its specificity is detected using a cultured cell line or the like which expresses the gene is generally used.
When a novel G protein-coupled receptor is used as the target of disease treatment, it is highly possible that the subtype-specificity is important, so that discovery of a receptor family is important also in the case of the novel G protein-coupled receptor. The homology of amino acid sequences among independent G protein-coupled receptors is 20 to 25% as a whole, but when they form a receptor family, the homology significantly increases in general in the family; so that it is possible to presume whether they form a family or not, by comparing homology between two G protein-coupled receptors. It is possible to find novel G protein-coupled receptors which form a family, making use of such a means, and when a novel G protein-coupled receptor family is discovered, it will open a way for developing a drug for disease therapy because of the possibility of creating a subtype-specific agonist or antagonist.
The central nervous system transmits and controls various kinds of information using physiologically active substances represented by neurotransmitters. The G protein-coupled receptor is taking an important role in the signal transduction and control. Since many types of G protein-coupled receptor are present in the central nervous system, they are used as important therapeutic targets for diseases of the central nervous system. For example, it is considered that the G protein-coupled receptor of a neurotransmitter, dopamine, is a therapeutic target of schizophrenia (Seeman, P. et al. (1997), Neuropsychopharmacology, 16, 93-110), the G protein-coupled receptor of serotonin is that of depression (Cowen, P. J. (1991), Br. J. Psychiatry, 159 (Suppl. 12), 7-14), and the G protein-coupled receptor of neuro-peptide Y is that of eating disorder (Blomqvist, A. G. and Herzog, H. (1997), Trends Neurosci., 20, 294-298).
It is considered that a novel G protein-coupled receptor expressing in the central nervous system, preferably a human receptor, will lead to a candidate for a new therapeutic target of central nervous system diseases or to the elucidation of central nervous system functions. In addition, for the purpose of developing a subtype-specific drug, it is desirable also to find a family in the case of the novel G protein-coupled receptor expressing in the central nervous system. Though the gene of a receptor GPR27 obtained from a mouse, having high homology with the amino acid sequence of SREB1 which is one of the G protein-coupled receptors of the invention, and an amino acid sequence based on its gene sequence have been reported (O""Dowd, B. F. et al. (1998), Genomics, 47, 310-313), no information is available to date concerning gene sequence and amino acid sequence of a human receptor.
The present invention is to provide novel G protein-coupled receptor family proteins expressed in the central nervous system, as the target of therapeutic agents for central nervous system diseases.
With the aim of achieving the above object, the present inventors have conducted intensive studies and, as a result, succeeded in isolating genes (SREB1, SREB2, SREB3, rSREB1, rSREB2 and rSREB3) which encode novel G protein-coupled receptor family proteins expressed in the central nervous system.
Also, we have established vectors containing these genes, host cells containing these vectors and methods for producing these G protein-coupled receptor proteins using such host cells, and rendered possible screening of these G protein-coupled receptor proteins and compounds, peptides and antibodies capable of modifying activities of the G protein-coupled receptor proteins.
Illustratively, the present invention relates to
(1) a G protein-coupled receptor protein which has the amino acid sequence described in SEQ ID NOs: 2, 4, 6, 22 or 26, or a G protein-coupled receptor protein as an equivalent to the protein, preferably a human origin G protein-coupled receptor protein which has the amino acid sequence described in SEQ ID NOs: 2, 4 or 6 or a G protein-coupled receptor protein as an equivalent to the protein, or a rat origin G protein-coupled receptor protein which has the amino acid sequence described in SEQ ID NOs: 6, 22 or 26 or a G protein-coupled receptor protein as an equivalent to the protein,
(2) a G protein-coupled receptor protein which has the amino acid sequence described in SEQ ID NOs: 2, 4, 6, 22 or 26,
(3) a gene which has a nucleotide sequence coding for the G protein-coupled receptor protein described in the item (1),
(4) a vector which contains the gene described in the item (3),
(5) a host cell which contains the vector described in the item (4),
(6) a method for producing the G protein-coupled receptor protein described in the item (1) or (2), or a G protein-coupled receptor protein as an equivalent to the protein, which comprises using the host cell described in the item (5),
(7) a method for screening a medicament acting on the G protein-coupled receptor protein described in the item (1) or (2), which comprises allowing the G protein-coupled receptor protein to contact with a compound to be tested, or
(8) an antibody for the G protein-coupled receptor protein described in the item (1) or (2) or a partial peptide thereof.
The following explains the terms to be used herein.
The term xe2x80x9chuman originxe2x80x9d or xe2x80x9crat originxe2x80x9d means an amino acid sequence identical to the amino acid sequence of a G protein-coupled receptor protein expressing in human or rat.
The term xe2x80x9cequivalentxe2x80x9d of the G protein-coupled receptor protein of the present invention means a G protein-coupled receptor protein which is expressed in the central nervous system and shows the same activity of any one of the G protein-coupled receptor proteins represented by the amino acid sequences described in SEQ ID NOs: 2, 4, 6, 22 or 26.
In this connection, the G protein-coupled receptor and the G protein-coupled receptor protein have the same meaning.
The novel G protein-coupled receptor protein of the present invention is any one of the G protein-coupled receptor proteins represented by the amino acid sequences described in SEQ ID NOs: 2, 4, 6, 22 and 26, or equivalents thereof. Illustratively, all of G protein-coupled receptor proteins are included in the invention as long as they have the amino acid sequence described in SEQ ID NOs: 2, 4, 6, 22 or 26, or an amino acid sequence in which the amino acid sequence described in SEQ ID NOs: 2, 4, 6, 22 or 26, has substitution, deletion or insertion of one or a plurality, preferably from 1 to 10, more preferably from 1 to 7, most preferably from 1 to 5, of amino acids, and have the same activity of the protein represented by the amino acid sequence described in SEQ ID NOs: 2, 4 or 6. Preferably, it is a human or rat origin G protein-coupled receptor protein having the amino acid sequence described in SEQ ID NOs: 2, 4, 6, 22 or 26.
Also, the gene which has a nucleotide sequence coding for the novel G protein-coupled receptor protein of the invention may be any gene, as long as it has a nucleotide sequence coding for the G protein-coupled receptor protein represented by the amino acid sequence described in SEQ ID NOs: 2, 4 or 6, or an equivalent thereof. Preferably, it is a gene which has a nucleotide sequence coding for the amino acid sequence described in SEQ ID NOs: 2, 4, 6, 22 or 26. More preferably, it is a gene which has a sequence of from 1 to 1,125 positions of the nucleotide sequence described in SEQ ID NO: 1, from 1 to 1,110 positions of the nucleotide sequence described in SEQ ID NO: 3, from 1 to 1,119 positions of the nucleotide sequence described in SEQ ID NO: 5, from 1 to 1,131 positions of the nucleotide sequence described in SEQ ID NO: 21, from 1 to 1,110 positions of the nucleotide sequence described in SEQ ID NO: 23 or from 1 to 1,119 positions of the nucleotide sequence described in SEQ ID NO: 25.
The gene which encodes the G protein-coupled receptor protein of the invention can be obtained by the following methods.
1) Production Methods of Novel G Protein-Coupled Receptor Protein Gene
a) First Production Method
A mRNA sample is extracted from human cells or tissue having the ability to produce the G protein-coupled receptor protein of the invention. Next, using this mRNA as the template, two primers interposing the G protein-coupled receptor protein mRNA or a part of the mRNA region is prepared. The G protein-coupled receptor protein cDNA or a part thereof can be obtained by carrying out a reverse transcriptase-polymerase chain reaction (to be referred to as RT-PCR hereinafter) suited for SREB1, SREB2 or SREB3 by modifying the conditions for denature temperature, denaturing agent addition and the like. Thereafter, the receptor protein can be produced by integrating the thus obtained G protein-coupled receptor cDNA or a part thereof into an appropriate expression vector and expressing it in a host cell.
Firstly, mRNA molecules including those encoding the G protein-coupled receptor protein of the invention are extracted by a known method from cells or tissue, such as of the human brain or rat brain, having the ability to produce the protein. Regarding the extraction method, a guanidine thiocyanate hot phenol method, a guanidine thiocyanate-guanidine hydrochloride method and the like can be exemplified, and a guanidine thiocyanate cesium chloride method can be cited as a preferred method. The cells or tissue having the ability to produce the protein can be identified by the Northern blotting method using a gene having a nucleotide sequence coding for the protein or a part thereof or by the Western blotting method using an antibody specific for the protein.
Purification of mRNA can be carried out in accordance with the conventional method, for example by adhering the mRNA to an oligo(dT) cellulose column and then eluting it therefrom. In addition, the mRNA can be further fractionated, for example, by a sucrose density gradient centrifugation. Alternatively, a commercially available already-extracted mRNA preparation may be used without carrying out the mRNA extraction.
Next, a single-stranded cDNA is synthesized from the thus purified mRNA by carrying out a reverse transcriptase reaction in the presence of a random primer or an oligo-dT primer. This synthesis can be carried out in the conventional way. The novel G protein-coupled receptor DNA of interest is amplified by subjecting the thus obtained single-stranded cDNA to PCR using two primers interposing a region of the gene of interest. The thus obtained DNA is fractionated, for example, by an agarose gel electrophoresis. As occasion demands, a DNA fragment of interest can be obtained by digesting the DNA with restriction enzymes and then connecting the digests.
b) Second Production Method
In addition to the above method, the gene of the invention can also be produced making use of conventional genetic engineering techniques. Firstly, single-stranded cDNA is synthesized using the mRNA obtained by the above method as the template and a reverse transcriptase, and then double-stranded cDNA is synthesized from the single-stranded cDNA. Examples of the method include the S1 nuclease method (Efstratiadis, A. et al. (1976), Cell, 7, 279-288), the Land method (Land, H. et al. (1981), Nucleic Acids Res., 9, 2251-2266), the O. Joon Yoo method (Yoo, O. J. et al. (1983), Proc. Natl. Acad. Sci. USA, 79, 1049-1053) and the Okayama-Berg method (Okayama, H. and Berg, P. (1982), Mol. Cell. Biol., 2, 161-170).
Next, the recombinant plasmid obtained by the above method is introduced into an Escherichia coli strain, such as DH5xcex1, to effect its transformation, and a transformant can be selected making use of tetracycline resistance or ampicillin resistance as a marker. For example, when the host cell is Escherichia coli, transformation of the host cell can be carried out by the Hanahan""s method (Hanahan, D. (1983), J. Mol. Biol., 166, 557-580), namely a method in which the recombinant DNA is added to competent cells prepared in the presence of CaCl2 and MgCl2 or RbCl. In this case, not only a plasmid but also a lambda or the like phage vector can also be used as the vector.
A strain having DNA coding for the novel G protein-coupled receptor protein of interest can be selected from the thus obtained transformants, for example by the following various methods.
(1) A Screening Method which Uses a Synthetic Oligonucleotide Probe
An oligonucleotide corresponding to the entire portion or a part of the G protein-coupled receptor protein of the invention is synthesized (in this case, it may be either a nucleotide sequence derived using the codon usage or a combination of plural possible nucleotide sequences, and in the latter case, their kinds can be reduced by including inosine), this is used as a probe (labeled with 32P or 33P) and allowed to hybridize with DNA samples of transformants, which are denatured and fixed on a nitrocellulose filter, and then a positive strain is screened and selected.
(2) A Screening Method Which Uses a Probe Prepared by Polymerase Chain Reaction
Sense primer and antisense primer oligonucleotides corresponding to a part of the G protein-coupled receptor protein of the invention are synthesized, and polymerase chain reaction (Saiki, R. K. et al. (1988), Science, 239, 487-491) is carried out using a combination of them to effect amplification of a DNA fragment of interest coding for the entire portion or a part of the G protein-coupled receptor protein. As the template DNA to be used herein, cDNA synthesized by the reverse transcription reaction from mRNA of cells capable of producing the G protein-coupled receptor protein or genomic DNA can be used. The thus prepared DNA fragment is labeled with 32P or 33P and used as the probe to select a clone of interest by carrying out colony hybridization or plaque hybridization.
(3) A Screening Method in Which the Novel G Protein-coupled Receptor Protein is Produced in Other Animal Cells
A transformant is cultured to amplify the gene of interest, the gene is transfected into an animal cell (in this case, either a plasmid which can perform autonomous replication and contains a transcription promoter region or a plasmid which can be integrated into chromosome of the animal cell may be used) and a protein coded by the gene is produced on the cell surface. By detecting the protein using an antibody specific for the G protein-coupled receptor protein of the invention, a strain of interest having cDNA coding for the G protein-coupled receptor protein is selected from the original transformants.
(4) A Selection Method Which Uses an Antibody Specific for the G Protein-coupled Receptor Protein of the Invention
In advance, cDNA is integrated into an expression vector and protein is produced on the surface of transformant strains, and then strains capable of producing the G protein-coupled receptor protein are detected using an antibody specific for the G protein-coupled receptor protein of the invention and a second antibody for the first antibody, thereby selecting a strain of interest.
(5) A Method Which Uses a Selective Hybridization Translation System
Samples of cDNA obtained from transformants are blotted on, for example, a nitrocellulose filter and hybridized with mRNA prepared from cells capable of producing the G protein-coupled receptor protein of the invention, and then the mRNA linked to the cDNA is dissociated and recovered. The thus recovered mRNA is then translated into protein using a protein translation system, for example by injecting into Xenopus oocyte or in a cell-free system such as a rabbit reticulocyte lysate, wheat germ or the like. A strain of interest is selected by detecting it using an antibody for the G protein-coupled receptor protein of the invention.
Collection of DNA which encodes the G protein-coupled receptor protein of the invention from the thus obtained transformant of interest can be carried out in accordance with a known method (Maniatis, T. et al. (1982): xe2x80x9cMolecular Cloningxe2x80x94A Laboratory Manualxe2x80x9d, Cold Spring Harbor Laboratory, NY). For example, it can be carried out by separating a fraction corresponding to a plasmid DNA from cells, and cutting out a cDNA region from the plasmid DNA.
c) Third Production Method
The gene which has a nucleotide sequence coding for the amino acid sequence represented by SEQ ID NOs: 2, 4, 6, 22 or 26 can also be produced by binding DNA fragments produced by a chemical synthesis method. Each DNA can be synthesized using a DNA synthesizer (e.g., Oligo 1000M DNA Synthesizer (Beckman), 394 DNA/RNA Synthesizer (Applied Biosystems) or the like).
d) Fourth Production Method
For the purpose of effecting expression of the function of G protein-coupled receptor protein of the invention by the substance thus obtained by genetic engineering techniques making use of the gene of the invention, it is not always necessary to have all of the amino acid sequences represented by SEQ ID NOs: 2, 4, 6, 22 and 26; for example, even if it is a partial sequence or other amino acid sequence is added thereto, such proteins are also included in the G protein-coupled receptor protein of the invention, as long as they show the same activity of the G protein-coupled receptor protein represented by the amino acid sequence shown in SEQ ID NOs: 2, 4, 6, 22 or 26. Also, as is known by the interferon gene and the like, it is considered that genes of eucaryote generally show polymorphism (e.g., see Nishi, T. et al. (1985), J. Biochem., 97, 153-159), and there is a case in which one or a plurality of amino acid are substituted by this polymorphism or a case in which the nucleotide sequence is changed but the amino acids are completely unchanged. In consequence, even in the case of proteins in which one or a plurality of amino acid residues are substituted, deleted or inserted at one or a plurality of positions in the amino acid sequence represented by SEQ ID NOs: 2, 4 or 6, it is possible that they have the same activity of the G protein-coupled receptor represented by the amino acid sequence described in SEQ ID NOs: 2, 4 or 6. These proteins are called equivalents to the G protein-coupled receptor protein of the invention and included in the invention. In addition, a G protein-coupled receptor having the rat origin amino acid sequence shown by SEQ ID NOs: 22, 24 or 26 or a G protein-coupled receptor having the same activity of the former receptor is also included in the equivalents.
All of the genes having nucleotide sequences which encode these equivalents to the G protein-coupled receptor protein of the invention are included in the invention. Such various genes of the invention can also be produced by nucleic acid chemical synthesis methods in accordance with a usual method such as the phosphite triester method (Hunkapiller, M. et al. (1984), Nature, 10, 105-111), based on the information on the G protein-coupled receptor protein of the invention described in the foregoing. In this connection, codons for desired amino acid are well known, and they can be optionally selected and determined in the usual way, for example by taking codon usage of the host to be used into consideration (Crantham, R. et al. (1981), Nucleic Acids Res., 9, r43-r74). In addition, partial modification of codons of these nucleotide sequences can be carried out in the usual way in accordance, for example, with the site specific mutagenesis (Mark, D. F. et al. (1984), Proc. Natl. Acad. Sci. USA, 81, 5662-5666) which uses a primer comprised of a synthetic oligonucleotide coding for the desired modification.
Determination of the sequence of DNA obtained by the above methods a) to d) can be carried out by, for example, the Maxam-Gilbert chemical modification method (Maxam, A. M. and Gilbert, E. (1980): xe2x80x9cMethods in Enzymologyxe2x80x9d, 65, 499-559) or the dideoxy nucleotide chain termination method (Messing, J. and Vieira, J. (1982), Gene, 19, 269-276) which uses M13.
Also, the vector of the invention, the host cell of the invention and the G protein-coupled receptor protein of the invention can be obtained by the following methods.
2) Production Method of Recombinant Protein of the G Protein-coupled Receptor of the Invention
An isolated fragment containing a gene coding for the G protein-coupled receptor protein of the invention can transform other eucaryotic host cell by again integrating into an appropriate vector DNA. In addition, it is possible to express the gene in respective host cells by introducing an appropriate promoter and a sequence related to the gene expression into these vectors.
Cells of vertebrates, insects, yeast and the like are included in the eucaryotic host cells and, though not particularly limited, examples of commonly used vertebrate cells include COS cell which is a simian cell (Gluzman, Y. (1981), Cell, 23, 175-182), a dihydrofolate reductase deficient strain of Chinese hamster ovary cell (CHO) (Urlaub, G. and Chasin, L. A. (1980), Proc. Natl. Acad. Sci. USA, 77, 4216-4220), human fetal kidney HEK293 cell and 293-EBNA cell (Invitrogen) prepared by introducing Epstein Barr virus EBNA-1 gene into the human cell.
As the expression vector for vertebrate cells, a vector which contains a promoter positioned on the upstream of the gene to be expressed, an RNA splicing site, a polyadenylation site, transcription termination sequence and the like can generally be used, and it may further contain a replication origin as occasion demands. Examples of the expression vector include pSV2dhfr having SV40 early promoter (Subramani, S. et al. (1981), Mol. Cell. Biol., 1, 854-864), pEF-BOS having human elongation factor promoter (Mizushima, S. and Nagata, S. (1990), Nucleic Acids Res., 18, 5322), pCEP4 having cytomegalovirus promoter (Invitrogen) and the like, though not limited thereto.
In a case in which COS cell is used as the host cell, an expression vector which has SV40 replication origin, can perform autonomous growth in COS cell and has a transcription promoter, a transcription termination signal and an RNA splicing site can be used, and its examples include pME18S (Maruyama, K. and Takebe, Y. (1990), Med. Immunol., 20, 27-32), pEF-BOS (Mizushima, S. and Nagata, S. (1990), Nucleic Acids Res., 18, 5322), pCDM8 (Seed, B. (1987), Nature, 329, 840-842) and the like. The expression vector can be incorporated into COS cell by, for example, the DEAE-dextran method (Luthman, H. and Magnusson, G. (1983), Nucleic Acids Res., 11, 1295-1308), the calcium phosphate-DNA co-precipitation method (Graham, F. L. and van der Ed., A. J. (1973), Virology, 52, 456-457), a method which uses FuGENE6(trademark) (Boeringer Mannheim) or the electroporation method (Neumann, E. et al. (1982), EMBO J., 1, 841-845), and a desired transformant cell can thus be obtained.
Also, when CHO cell is used as the host cell, a transformant cell capable of stably producing the novel G protein-coupled receptor protein can be obtained by carrying out co-transfection of an expression vector together with a vector capable of expressing neo gene which functions as a G418 resistance marker, such as pRSVneo (Sambrook, J. et al. (1989): xe2x80x9cMolecular Cloningxe2x80x94A Laboratory Manualxe2x80x9d, Cold Spring Harbor Laboratory, NY) or pSV2-neo (Southern, P. J. and Berg, P. (1982), J. Mol. Appl. Genet., 1, 327-341), and selecting a G418 resistant colony. In addition, when 293-EBNA cell is used as the host cell, a desired transformant cell can be obtained using an expression vector which has Epstein Barr virus replication origin and can perform autonomous growth in the 293-EBNA cell, such as pCEP4 (Invitrogen).
The thus obtained desired transformant can be cultured in the conventional way, and the G protein-coupled receptor protein of the invention is produced inside the cells or on the cell surface by this culturing. Regarding the medium to be used in this culturing, it can be optionally selected from various commonly used media depending on each host cell employed; for example, in the case of the COS cell, RPMI-1640 medium, Dulbecco""s modified Eagle""s minimum essential medium (DMEM) or the like can be used by adding serum components such as fetal bovine serum (FBS) and the like as occasion demands. Also, in the case of the 293-EBNA cell, Dulbecco""s modified Eagle""s minimum essential medium (DMEM) or the like medium supplemented with serum components such as fetal bovine serum (FBS) and the like can be used by further adding G418.
The G protein-coupled receptor protein of the invention thus produced inside the cell or on the cell surface of the transformant can be separated and purified therefrom by various known separation techniques making use of physical properties, chemical properties and the like of the receptor protein. Illustrative examples of such techniques, to be carried out after solubilization of the receptor protein-containing membrane fraction, include usual treatment with a protein precipitant, ultrafiltration, various liquid chromatography means such as molecular sieve chromatography (gel filtration), adsorption chromatography, ion exchange chromatography, affinity chromatography, high performance liquid chromatography (HPLC) and the like, dialysis and combinations thereof. In this connection, the membrane fraction can be obtained in the usual way. For example, it can be obtained by culturing the cells which expressed the G protein-coupled receptor protein on the surface, suspending them in a buffer and then homogenizing and centrifuging them. Also, when the G protein-coupled receptor protein is solubilized using a solubilizing agent as mild as possible (CHAPS, Triton(copyright) X-100, digitonin or the like), characteristics of the receptor can be maintained after the solubilization.
By effecting expression of the G protein-coupled receptor protein of the invention through its in-frame fusion with a marker sequence, confirmation of the expression the G protein-coupled receptor protein, confirmation of its intracellular localization, purification thereof and the like become possible. Examples of the marker sequence include FLAG(copyright) epitope, Hexa-Histidine tag, Hemagglutinin tag, myc epitope and the like. Also, when a specific sequence recognizable by a protease such as enterokinase, factor Xa or thrombin is inserted between a marker sequence and the G protein-coupled receptor protein, the marker sequence can be cut and removed by such a protease. For example, there is a report in which muscarinic acetylcholine receptor and Hexa-Histidine tag are connected with a thrombin-recognizing sequence (Hayashi, M. K. and Haga, T. (1996), J. Biochem., 120, 1232-1238).
A method for the screening of compounds, peptides and antibodies capable of modifying activity of the G protein-coupled receptor protein is included in the invention. This screening method comprises adding an agent to be tested to a system in which an index of the modification of G protein-coupled receptor protein in response to a physiological characteristic of the G protein-coupled receptor protein is measured making use of the thus constructed G protein-coupled receptor protein, and measuring the index. The following screening methods can be cited as illustrative examples of this measuring system. Also, examples of useful drugs to be tested include compounds or peptides which are conventionally known to have G protein-coupled receptor ligand activity but their ability to selectively modify activity of the novel G protein-coupled receptor protein is not clear, known compounds and peptides registered in chemical files but their various G protein-coupled receptor ligand activities are unknown, compounds obtained by the method such as combinatorial chemistry techniques (Terrett, N. K. et al. (1995), Tetrahedron, 51, 8135-8137) and random peptides prepared by employing a phage display (Felici, F. et al. (1991), J. Mol. Biol., 222, 301-310) or the like. In addition, culture supernatants of microorganisms, natural components originated from plants and marine organisms, animal tissue extracts and the like are also objects of the screening. Also useful are compounds or peptides obtained by chemically or biologically modifying a compound or peptide selected by the screening method of the invention.
3) Screening Methods of Ligands of the G Protein-coupled Receptor Protein of the Invention, Namely Compounds, Peptides and Antibodies which Modify Activity of the G Protein-coupled Receptor Protein of the Invention
a) A Screening Method which Uses a Ligand Binding Assay Method
Compounds, peptides and antibodies which bind to the G protein-coupled receptor protein of the invention (generally referred to as ligand) can be screened by a ligand binding assay method. A cell membrane sample obtained after expression of the receptor protein or a purified sample of the receptor protein is prepared, and a ligand purified for use in the ligand binding assay is radiation-labeled (50 to 2,000 Ci/mmol). Buffer solution, ions, pH and the like assay conditions are optimized, and the receptor protein-expressed cell membrane sample or the purified receptor protein sample is incubated in the thus optimized buffer for a predetermined period of time together with the radiation-labeled ligand. After the reaction, this is filtered through, e.g., a glass filter and washed with an appropriate amount of the buffer, and then the radioactivity remained on the filter (total binding amount) is measured using, e.g., a liquid scintillation counter. Nonspecific binding amount is measured by adding the unlabeled ligand in large excess in the reaction solution, and the specific binding amount is obtained by subtracting the nonspecific binding amount from the total binding amount. A ligand showing specific binding to the receptor protein-expressed cell membranes or the purified receptor protein can be selected as a ligand of the G protein-coupled receptor protein of the invention. In addition, a compound, peptide or antibody having agonist activity, or a compound, peptide or antibody having antagonist activity, of the G protein-coupled receptor protein can be screened making use of the binding inhibition of the thus obtained radioactive ligand as an index.
b) A Screening Method Which Uses a GTPxcex3S Binding Method
Compounds, peptides and antibodies capable of modifying the activity of the G protein-coupled receptor protein of the invention can be screened by a GTPxcex3S binding method (Lazareno, S. and Birdsall, N. J. M. (1993), Br. J. Pharmacol., 109, 1120-1127). Cell membranes obtained after expression of the receptor protein is mixed with 400 pM of GTPxcex3S labeled with 35S in a solution of 20 mM HEPES (pH 7.4), 100 mM NaCl, 10 mM MgCl2 and 50 mM GDP. After incubation in the presence or absence of an agent to be tested, this is filtered through, e.g., a glass filter and then radioactivity of the bound GTPxcex3S is measured using, e.g., a liquid scintillation counter. A compound, peptide or antibody having agonist activity of the G protein-coupled receptor protein can be screened making use, as an index, of the increased specific GTPxcex3S binding in the presence of the drug to be tested. Also, a compound, peptide or antibody having antagonist activity of the G protein-coupled receptor protein can be screened making use, as an index, of the suppression of increase in the GTPxcex3S binding by the thus obtained compound, peptide or antibody having agonist activity.
c) A Screening Method Which Uses Changes in the Intracellular Ca++ and cAMP concentrations
Many G protein-coupled receptor proteins induce increase in Ca++ and/or increase or decrease in cAMP concentration in the cells caused by an agonist stimulus. Accordingly, compounds, peptides and antibodies capable of modifying the activity of the G protein-coupled receptor protein of the invention can be screened making use of the changes in the intracellular Ca++ or cAMP concentration. The Ca++ concentration is measured using fura2 and the like, and the cAMP concentration is measured using a commercially available cAMP assay kit (by Amersham, etc.).
Alternatively, it is possible to measure the Ca++ and cAMP concentrations indirectly, by detecting the transcription activity of a gene whose transcription amount is controlled depending on the Ca++ and cAMP concentrations. A sample such as a compound, a peptide, a tissue extract or the like is allowed to react for a predetermined period of time with cells in which the receptor protein is expressed or host cells in which the receptor protein is not expressed (control cells), and the Ca++ and cAMP concentrations are measured directly or indirectly. A compound, peptide or antibody having agonist activity can be screened making use, as an index, of the increase in Ca++ and/or increase or decrease in cAMP concentration in the receptor protein-expressed cells by comparing with the control cells. Also, a compound, peptide or antibody having antagonist activity of the G protein-coupled receptor protein can be screened making use, as an index, of the increase in Ca++ and/or increase or decrease in cAMP concentration caused by the thus obtained compound, peptide or antibody having agonist activity.
d) A Screening Method Which Uses Microphysiometer
Upon various signal responses of cells, trace amount of hydrogen ions outflow into the extracellular moiety is detected. Most of this outflow of hydrogen ions occur when metabolites formed by the fuel consumption of cells to obtain energy for their responses are increased or when signals of the cells are transmitted directly to the hydrogen ion pump. Since the G protein-coupled receptor protein of the invention requires energy for its signal transmission, outflow of hydrogen ions occurs when the receptor is activated. Since changes in pH caused by such a trace outflow of hydrogen ions in a medium around cells can be detected by CYTOSENSOR(copyright) Microphysiometer (Molecular Devices), it can be used for the detection of the activation energy consuming receptors.
A compound, a peptide, a tissue extract or the like is allowed to react for a predetermined period of time with cells in which the receptor protein is expressed or host cells in which the receptor protein is not expressed (control cells), and changes in the pH due to outflow of hydrogen ions are measured. A compound, peptide or antibody having agonist activity can be screened making use, as an index, of the changes in pH caused by the outflow of hydrogen ions from the receptor protein-expressed cells by comparing with the control cells. Also, a compound, peptide or antibody having antagonist activity of the G protein-coupled receptor protein can be screened making use, as an index, of the changes in pH due to the outflow of hydrogen ions caused by the thus obtained compound, peptide or antibody having agonist activity.
A medicament which contains as the active ingredient a compound, peptide or antibody capable of significantly modifying the activity of the G protein-coupled receptor protein or a G protein-coupled receptor protein selected by the screening method is included in the invention.
The antibody, such as a polyclonal antibody or monoclonal antibody, which reacts with the G protein-coupled receptor protein of the invention can be obtained by directly administering the novel G protein-coupled receptor protein or a fragment of the G protein-coupled receptor protein to various animals. It can also be obtained by a DNA vaccine method (Raz, E. et al. (1994), Proc. Natl. Acad. Sci. USA, 91, 9519-9523; Donnelly, J. J. et al. (1996), J. Infect. Dis., 173, 314-320) using a plasmid in which a gene which encodes the G protein-coupled receptor protein of the invention is introduced.
The polyclonal antibody is produced from sera or eggs of an animal (e.g., rabbit, rat, goat, fowl or the like) immunized and sensitized by emulsifying the G protein-coupled receptor protein or a fragment thereof in an appropriate adjuvant such as complete Freund""s adjuvant and administering it by intraperitoneal, subcutaneous or intravenous injection. The polyclonal antibody thus produced from sera or eggs can be separated and purified by the usual protein isolation purification methods. Examples of such methods include centrifugation, dialysis, salting out with ammonium sulfate, and chromatographic techniques using carriers such as DEAE-cellulose, hydroxyapatite, protein A agarose and the like.
An active antibody fragment containing a part of the antibody, such as F(abxe2x80x2)2, Fab, Fabxe2x80x2 or Fv, can be obtained by digesting the thus separated and purified antibody with a proteolytic enzyme such as pepsin, papain or the like in the usual way and subsequently separating and purifying it by the usual protein isolation purification methods.
It is possible for those skilled in the art to easily produce a monoclonal antibody by the cell fusion method of Kohler and Milstein (Kohler, G. and Milstein, C. (1975), Nature, 256, 495-497).
Mice are immunized by intraperitoneal, subcutaneous or intravenous inoculation of an emulsion prepared by emulsifying the G protein-coupled receptor protein of the invention or a fragment thereof in an appropriate adjuvant such as complete Freund""s adjuvant, several times repeatedly at intervals of several weeks. After final immunization, spleen cells are collected and fused with myeloma cells to prepare a hybridoma.
Myeloma cells having hypoxanthine-guanine phosphoribosyltransferase deficiency, thymidine kinase deficiency or the like marker, such as mouse myeloma cell strain P3X63Ag8.U1, are used as the myeloma cells for obtaining the hybridoma. Also, polyethylene glycol is used as the fusing agent. In addition, Eagle""s minimum essential medium, Dulbecco""s modified minimum essential medium, RPMI-1640 or the like generally used medium is optionally supplemented with 10 to 30% of fetal bovine serum and used as the medium for the preparation of the hybridoma. Fused strains are selected by the HAT selection method. Screening of hybridoma is carried out using a conventional method such as the culture supernatant by ELISA, immunohistological staining or the like or by the screening method described in the foregoing, and a hybridoma clone secreting the antibody of interest is selected. Also, monoclonal nature of the hybridoma is confirmed by repeating subcloning by means of limiting dilution analysis. When the thus obtained hybridoma is cultured for 2 to 4 days in a medium or for 10 to 20 days in the abdominal cavity of a BALB/c mice pretreated with pristane, the antibody in an amount sufficient for purification is produced.
The thus produced monoclonal antibody can be separated and purified from the culture supernatant or ascites by the usual protein isolation purification methods. Examples of such methods include centrifugation, dialysis, salting out with ammonium sulfate, and chromatographic techniques using carriers such as DEAE-cellulose, hydroxyapatite, protein A agarose and the like. In addition, the monoclonal antibody or an antibody fragment containing a part thereof can also be produced by integrating entire portion or a part of a gene coding for the antibody into an expression vector and introducing into Escherichia coli, yeast or animal cells. An active antibody fragment containing a part of the antibody, such as F(abxe2x80x2)2, Fab, Fabxe2x80x2 or Fv, can be obtained by digesting the thus separated and purified antibody with a proteolytic enzyme such as pepsin, papain or the like in the usual way and subsequently separating and purifying it by the usual protein isolation purification methods.
In addition, it is possible to obtain an antibody capable of reacting with the G protein-coupled receptor protein of the invention as single chain Fv or Fab by the method of Clackson et al. or Zebedee et al. (Clackson, T. et al. (1991), Nature, 352, 624-628; Zebedee, S. et al. (1992), Proc. Natl. Acad. Sci. USA, 89, 3175-3179). It is also possible to obtain a human antibody by immunizing a transgenic mouse in which a mouse antibody gene is replaced by a human antibody gene (Lonberg, N. et al. (1994), Nature, 368, 856-859).
The medicament of the invention is characterized in that it has a novel pharmacological action to selectively control activity of the G protein-coupled receptor, and examples of the use of the medicament include central nervous system diseases which are induced by abnormalities of the G protein-coupled receptor activity (acceleration, reduction, denaturation and the like) or which express the abnormalities as complications.
The pharmaceutical preparation which contains a compound, peptide, antibody or antibody fragment capable of modifying activity of the G protein-coupled receptor protein of the invention, as the active ingredient, can be prepared using carriers, fillers and other additives generally used in the preparation of medicaments, in response to each type of the active ingredient.
Examples of its administration include oral administration in the form of tablets, pills, capsules, granules, fine granules, powders, oral solutions and the like, and parenteral administration in the form of intravenous, intramuscular and the like injections, suppositories, percutaneous preparations, transmucosal absorption preparations and the like. Particularly, in the case of peptides which are digested in the stomach, intravenous injection or the like parenteral administration is desirable.
In the solid composition for use in the oral administration according to the present invention, one or more active substances are mixed with at least one inert diluent such as lactose, mannitol, glucose, microcrystalline cellulose, hydroxypropylcellulose, starch, polyvinyl pyrrolidone or aluminum magnesium metasilicate. In the usual way, the composition may contain additives other than the inert diluent, for example, a lubricant, a disintegrating agent, a stabilizing agent and a solubilizing or solubilization assisting agent. If necessary, tablets or pills may be coated with a sugar coating or a film of a gastric or enteric substance.
The liquid composition for oral administration includes emulsions, solutions, suspensions, syrups and elixirs and contains a generally used inert diluent such as purified water or ethanol. In addition to the inert diluent, this composition may also contain other additives such as moistening agents, suspending agents, sweeteners, flavors and antiseptics.
The injections for parenteral administration includes aseptic aqueous or non-aqueous solutions, suspensions and emulsions. Examples of the diluent for use in the aqueous solutions and suspensions include distilled water for injection use and physiological saline. Examples of the diluent for use in the non-aqueous solutions and suspensions include propylene glycol, polyethylene glycol, plant oils (e.g., olive oil), alcohols (e.g., ethanol), polysorbate 80 and the like. Such a composition may further contain a moistening agent, an emulsifying agent, a dispersing agent, a stabilizing agent, a solubilizing or solubilization assisting agent, an antiseptic and the like. These compositions are sterilized for example by filtration through a bacteria retaining filter, blending of a germicide or irradiation. Alternatively, they may be used by firstly making into sterile solid compositions and dissolving them in sterile water or other sterile solvent for injection use prior to their use.
The dose is optionally decided by taking into consideration strength of each active ingredient selected by the screening method described in the foregoing and symptoms, age, sex and the like of each patient to be administered.